Recently, a method for forming a tire using a rigid core has been proposed to enhance accuracy in forming the tire (refer to, for example, patent documents 1 and 2). The rigid core includes a core body having an external shape corresponding to a shape of a tire inner cavity surface of the tire after being subjected to vulcanization. Tire structural members are sequentially stuck onto the core body so as to form a green tire. The green tire, together with the rigid core, is then put into a vulcanization mold. And, the green tire is vulcanization-molded while being held between the core body as an inner mold and the vulcanization mold as an outer mold.
As shown in FIG. 8(A), the core body (a) is composed of a plurality of circumferentially divided core segments (c) so as to be disassembled and removed from the tire after the vulcanization molding. Using both circumferential end surfaces of each of the core segments (c) as mating surfaces (cs), the mating surfaces (cs) adjacent to each other in the circumferential direction are abutted against each other, and thereby the core body in an annular shape is formed.
As shown in FIG. 8(B), the mating surface (cs) of a conventional core segment (c) is formed in a planar shape. The mating surface (cs) is constructed so that its entirety contacts with the adjacent mating surface (cs). Therefore, effect of the flatness of the mating surface (cs) is increased, causing problems such that roundness of the core body (a) is lowered. And a gap is formed between the mating surfaces (cs) and intrusion of rubber is occurred.
In particular, the core body (a) is subjected to a temperature rise from a normal temperature state during the formation of the green tire (approximately 15 to 50 degrees C.) to a high temperature state during the vulcanization molding (100 degrees C. or above). Further, a circumferential length of a tread region is longer than a circumferential length of a bead region. Consequently, a tread side is subject to a large amount of thermal expansion, and a bead side is subject to a small amount of thermal expansion. Therefore, the mating surfaces (cs) during the vulcanization may be complicatedly deformed in an undulating shape, resulting in significant deterioration of the flatness. This can increase the number of regions including a gap between the mating surfaces (cs), and can also enlarge the gap between the mating surfaces (cs) during the vulcanization. Hence there has been the problem that the intrusion of rubber becomes more severe and pressing force between the core segments (c) becomes uneven, and therefore the roundness of the core body (a) is apt to deteriorate.
Patent document 1: Japanese unexamined Patent Application No. 2011-161896.
Patent document 2: Japanese Unexamined Patent Application No. 2011-167979.